Particular attention is required whenever the word "about" or similar terms such as "approximately" or "substantially" are used. Such a word may be applied, for example, to a particular value (e.g. "about 200°C"), to a range (e.g. "about x to about y") or to a structural unit of an apparatus (e.g. "a tray plate with a substantially circular circumference"). In each case, the examiner should use his judgment as to whether the meaning is sufficiently clear in the context of the application read as a whole, and having regard to the meaning a particular technical term qualified by such a word usually has in the field concerned. If such words mean that a certain effect or result can be obtained within a certain tolerance and the skilled person knows how to obtain the tolerance, then the use of such words may be acceptable. If, however, the use of such a word suggests that deviations are included which are larger than those accepted tolerances, then the wording becomes vague and undefined. In any case, the word can only be permitted if its presence does not prevent the invention from being unambiguously distinguished from the prior art with respect to novelty and inventive step.